It has long been a goal in the tobacco art to find methods of expanding tobacco in order to increase the bulk or volume of the tobacco. There have been various reasons for expanding tobacco. One of the early purposes for expanding tobacco involved making up the loss of weight of the tobacco which occurred during the curing process. Another purpose was to improve the smoking characteristics of particular tobacco components, in particular, tobacco stems. It has also been desired to increase the filling power of tobacco so that a smaller amount of tobacco would be required to produce a smoking product, such as a cigarette, which would have the firmness and yet would produce lower tar and nicotine than the comparable smoking product made of non-expanded tobacco having a more dense tobacco filler.
Various methods have been proposed for expanding tobacco, including the impregnation of tobacco with a gas under pressure and the subsequent release of the pressure, whereby the gas causes expansion of the tobacco cells to increase the volume of the treated tobacco. Other methods which have been employed or suggested for the expansion of tobacco relate to the treatment of tobacco with various liquids, such as water or relatively volatile organic liquids, to impregnate the tobacco with the same, after which the liquids are volatilized to expand the tobacco. Additional methods which have been suggested relate to the treatment of tobacco with solid materials which, when heated, decompose to produce gases which serve to expand the tobacco. Other methods relate to the treatment of tobacco with gas-containing liquids, such as carbon dioxide-containing water, under pressure, to incorporate the gas in the tobacco, after which the tobacco impregnated therewith is heated or the pressure thereon is reduced to thereby expand the tobacco. Other methods have been suggested for expanding tobacco involving the treatment of tobacco with gases which react to form solid chemical reaction products within the tobacco, after which the solid reaction products may be decomposed by heat to produce gases within the tobacco which cause expansion of the tobacco upon their release. Illustrative of the art relating to tobacco expansion are the following:
U.S. Pat. No. 1,789,435, granted in 1931 to Wilford J. Hawkins, which describes a method and apparatus for expanding the volume of tobacco in order to make up the loss of weight caused in curing tobacco leaf. To accomplish this object, the cured and conditioned tobacco is contacted with a gas, which may be air, carbon dioxide or steam under pressure and the pressure is then relieved, whereby the tobacco tends to expand. The patent states that the volume of the tobacco may, by that process, be increased to the extent of about 5-15 percent.
Alien Property Custodian document No. 304,214 to Hoachim Bohme, dated 1943, indicates that tobacco can be expanded using a high frequency generator but that there are limitations to the degree of expansion which can be achieved without affecting the quality of the tobacco.
A patent to Frank J. Sowa, U.S. Pat. No. 2,596,183, granted in 1952, sets forth a method for increasing the volume of shredded tobacco by adding additional water to the tobacco to cause the tobacco to swell and thereafter heating the moisture containing tobacco, whereby the moisture evaporates and the resulting moisture vapor causes expansion of the tobacco.
A series of patents to Roger Z. de la Burde, one of the present coinventors, granted in 1968, specifically U.S. Pat. Nos. 3,409,022, 3,409,023, 3,409,027 and 3,409,028, relate to various processes for enhancing the utility of tobacco stems for use in smoking products by subjecting the stems to expansion operations utilizing various types of heat treatment or microwave energy.
A patent to John D. Hind, granted in 1969, U.S. Pat. No. 3,425,425, which is assigned to the same assignee as the assignee of the present invention, relates to the use of carbohydrates to improve the expansion of tobacco stems. In that process, tobacco stems are soaked in an aqueous solution of carbohydrates and then heated to puff the stems. The carbohydrate solution may also contain organic acids and/or certain salts which are used to improve the flavor and smoking qualities of the stems.
A publication in the "Tobacco Reporter" of November 1969 by P. S. Meyer relates to the art, as of that date, pertaining to tobacco puffing or expansion procedures or investigations for expanding and manipulating tobacco for purposes of reducing costs and also as the means for reducing the "tar" content by reduction in the delivery of smoke. Mention is made in this publication of puffing tobacco by different procedures including the use of halogenated hydrocarbons, low pressure or vacuum operation, or high pressure steam treatment that causes leaf expansion from inside the cell when outside pressure is suddenly released. Mention is also made in this publication of freeze-drying tobacco which can also be emloyed to obtain an increase in volume.
Since the above-mentioned Tobacco Reporter article was published, a number of tobacco expansion techniques, including some of the techniques described in the article, have been described in patents and/or published patent applications. For example:
U.S. Pat. No. 3,524,452 to Glenn P. Moser et al. and U.S. Pat. No. 3,524,451 to James D. Frederickson, both issued in 1970, relate to the expansion of tobacco using a volatile organic liquid, such as a halogenated hydrocarbon.
U.S. Pat. No. 3,734,104 to William M. Buchanan et al., which is assigned to the same assignee as the assignee of the present invention, issued in 1973, relates to a particular process for the expansion of tobacco stems.
U.S. Pat. No. 3,710,803 to William H. Johnson, issued in 1973 and British Specification No. 1,293,735 to American Brands, Inc., published in 1972, both relate to freeze drying methods for expanding tobacco.
South African application Nos. 70/8291 and 70/8282 to R. J. Reynolds Tobacco Company, both issued in 1970, relate to tobacco expansion employing chemical compounds which decompose to form a gas or with inert solutions of a gas under pressure to maintain the gas in solution until it impregnates the tobacco.
U.S. Pat. No. 3,771,533, issued in 1973 to Robert G. Armstrong et al., which is assigned to the same assignee as the assignee of the present invention, involves a treatment of tobacco with carbon dioxide and ammonia gases, whereby the tobacco is saturated with these gases and ammonium carbonate is formed in situ. The ammonium carbonate is thereafter decomposed by heat to release the gases within the tobacco cells and to cause expansion of the tobacco.
The use of special expanding agents, for example, halogenated hydrocarbons, such as are mentioned in the Meyer publication for expanding tobacco, is also not completely satisfactory because these substances are generally required to volatilize or remove the substances after the tobacco has been expanded. The introduction, in considerable concentration, of materials which are foreign to tobacco presents the problems of removing the expansion agent after the treatment has been completed in order to avoid affecting aroma and other properties of the smoke due to extraneous substances used or developed from the combustion of the treated tobacco.
The use of solid chemicals to produce a gas upon decomposition has not been found satisfactory, perhaps due to the fact that the chemicals cannot be incorporated in the cells of the tobacco.
The use of carbonated water has also not been found to be effective.
The present process has been found to overcome many of the disadvantages of the prior art processes and to provide an improved method for expanding tobacco, which employs water as the expanding medium.
One goal of workers in the art has been to cause substantial expansion of tobacco by employing water, alone, as the expansion method. The use of water, if it could be employed successfully, would have the advantage of incorporating no elements in the tobacco which could be used undesirably and of incorporating in the tobacco a degree of residual moisture which can be employed to satisfy the normal requirements, with respect to the degree of moisture employed in tobacco products. In general, the attempts which have been made to expand tobacco leaf with water, for example, by rapid heating or by sudden reduction of pressure, have not provided a permanent, usefully large degree of increase in volume. For example, the disclosure in U.S. Pat. No. 1,789,435 to Hawkins relates to the exposure of tobacco to high pressure steam, followed by sudden pressure release. The result has been found to consist of a poor quality tobacco with excessive breakage, and the volume increase is only 5 to 15 percent. Some processes involve alternate evacuation and steaming or moistening of tobacco but truly significant expansion has not been found to result from these. One of the present coinventors, de la Burde, has expanded tobacco stems with moisture alone (as described in U.S. Pat. Nos. 3,409,022; 3,409,023; 3,409,027 and 3,529,606) but the procedure has been found to have little effectiveness with leaf. Another technique which has been described is set forth in U.S. Pat. No. 3,710,803 to W. H. Johnson. This process, which was disclosed at the 23rd Tobacco Chemists Research Conference in October 1969, involves the expansion of tobacco by turgor conditioning followed by freeze drying. In accordance with the Johnson process, moisture content of the tobacco is brought to a level of 80 to 90 percent, by weight, before the freeze drying step, by evacuating the tobacco to remove air and water vapor, admitting liquid water to cover the tobacco while vacuum is maintained, then raising the pressure to atmospheric or above to drive the water rapidly into and between the cells. Johnson's sublimation drying is then carried out at a temperature of less than 32.degree.F. The Johnson process has been found to be of limited usefulness, in terms of commercial process, due to its inherent long processing time and its high cost, particularly in the drying step. In addition, the structure of the swollen tobacco produced by the process has been found to be subject to collapse due to the fact that when the water is not in solid form, during vacuum release, there is inadequate support for the swollen structure of the tobacco. Furthermore, the Johnson process can result in wash out or redistribution of water solubles. Thus, despite all of the above-described teachings, no completely satisfactory process has been found for the expansion of tobacco, whereby significant expansion can be obtained without the use of elaborate and expensive equipment and without the necessity for high operating costs.